From 50a48dad5579d67d7cae350f6ad5ae5c33f56abb Mon Sep 17 00:00:00 2001
From: Mark Shannon <mark@hotpy.org>
Date: Thu, 4 Jun 2020 13:23:35 +0100
Subject: [PATCH] Don't raise an exception on normal return from generator.
 (GH-19473)

---
 .../Core and Builtins/2020-04-11-13-07-49.bpo-4022.Ctpn_F.rst  | 1 +
 Objects/genobject.c                                            | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2020-04-11-13-07-49.bpo-4022.Ctpn_F.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-04-11-13-07-49.bpo-4022.Ctpn_F.rst b/Misc/NEWS.d/next/Core and Builtins/2020-04-11-13-07-49.bpo-4022.Ctpn_F.rst
new file mode 100644
index 00000000000..a13a8e88226
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-04-11-13-07-49.bpo-4022.Ctpn_F.rst	
@@ -0,0 +1 @@
+Improve performance of generators by not raising internal StopIteration.
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 09efbab69a7..1393f42533a 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -231,7 +231,8 @@ gen_send_ex(PyGenObject *gen, PyObject *arg, int exc, int closing)
             if (PyAsyncGen_CheckExact(gen)) {
                 PyErr_SetNone(PyExc_StopAsyncIteration);
             }
-            else {
+            else if (arg) {
+                /* Set exception if not called by gen_iternext() */
                 PyErr_SetNone(PyExc_StopIteration);
             }
         }